PHARMACOLOGICAL AND BIOCHEMICAL-CHARACTERIZATION OF CHOLECYSTOKININ GASTRIN RECEPTORS IN DEVELOPING RAT PANCREAS - AGE-RELATED EXPRESSION OF DISTINCT RECEPTOR GLYCOFORMS

Cholecystokinin/gastrin receptors in the pancreas of newborn (3-day-old) rats are of type A, as in control mature rats, revealed by pharmacological analysis of specific I-125-Bolton-Hunter-reagent-labelled [Thr34,Ahx37]cholecystokinin(31-39) (Ahx, aminohexanoic acid) binding. Also, by 1 day post-partum, pancreatic cholecystokinin receptors were shown to be coupled to guanine-nucleotide-binding regulatory (G) proteins. Scatchard analysis of I-125-Bolton-Hunter-reagent-labelled [Thr34,Ahx37]cholecystokinin(31-39) binding to pancreatic membranes from rats at different times after birth showed a slight increase in the binding capacity of cholecystokinin receptors between days 3 and 14 and a sixfold increase in 21-day-old rats, with no change in receptor affinity during development. SDS/PAGE analysis of pancreatic membranes affinity labelled with the photoactivable ligand I-125-[2-(p-azidosalicylamido)-1,3'-dithiopropionate]-labelled [Thr34,Ahx37]cholecystokinin-(31-39) identified cholecystokinin receptors of 100-135 kDa in 3-day-old rats, 96-130 kDa in 7-day-old rats, 90-125 kDa in 10-day-old rats and 85-100 kDa in 14-day-old and 21-day-old rats, as found in control adult rats. Endo-beta-N-acetylglucosaminidase F treatment yielded a core protein of 42 kDa in all developmental stages. These findings are consistent with an age-related postnatal expression of distinct glycoforms of pancreatic cholecystokinin receptors. Furthermore, it was observed that the period 2-3 weeks after birth, characterized by stabilization of the mass of the cholecystokinin receptor, precedes the dramatic increase in the receptor number.